A reed relay is a common type of relay. The reed relay includes one or more thin cantilevered metal arms or reeds made of paramagnetic material such as permalloy (typically, 80% nickel, 20% iron. In the presence of a magnetic field, the reeds experience a force and move to make contact with one another or another electrode to complete a circuit. Typical problems with reed relays are the requirements for high currents to latch and hold the connection and the high contact resistance that is present because of the relatively low force contact. Typical designs also suffer from poor radio frequency (RF) properties at greater than about 2 GHz because the un-terminated cantilevers act as antennas when the relay is open. An improvement to the typical reed relay is obtained by replacing the solid contacts with a thin mercury layer to reduce the contact resistance. This is typically known as a mercury film relay.
It is sometimes desirable to have a relay that can operate at speeds greater than 3 kHz. To increase the switching speed of a mechanical relay, the size of the mechanical relay typically needs to be scaled down in size to reduce inertia. MEMS (MicroElectroMechanical Systems) techniques have been adapted to produce a wide variety of small sized relays. Most such small sized relays have increased contact resistance because as the relay is scaled down in size the contact forces are also scaled down. Stiction forces increase as the relay is scaled down because surface forces scale with the area while restoring forces scale with the volume and stiction may become a problem if the devices are not handled appropriately during production and hermetically packaged. Mercury film relays typically cannot be significantly scaled down in size because of the surface tension forces that arise due to the smaller radius of the meniscus and act to prevent the relays from switching.